**19. Genetics of chronic cutaneous lupus erythematosus (CCLE)**

CCLE in the past referred to as discoid lupus represents the papulosquamous scarring form of cutaneous lupus erythematosus. Lupus panniculitis and lupus timidus also belong to this group. Lesions similar to these of CCLE have been described in carriers of the X-linked granulomatous disease [31]. Initial research found an association of HLA-A1, B8, HLA-B15, HLA-DRB10303 and HLA-DQA1 haplotype with CCLE.

#### *Lupus Genetics DOI: http://dx.doi.org/10.5772/intechopen.106372*

HLA-B8 was more frequently found in white CCLE patients while the HLA-DRW6 was found in an increased proportion of patients with DLE of both white and black races [32]. An association of HLA-DRB116 with CCLE in Mexican mestizo patients, the HLA-DRB116 gene is associated with most immune disorders mediated by the production of autoantibodies [33]. In a homozygous C2 deficiency patient with CCLE lupus, the C2 deficiency gene was associated with HLA-A10, B18, DR2, C4A4B2, Bfs, on one chromosome and with HLA-A2, B7 DR2, C4A4B2, Bfs on the other [34]. Susceptibility to CCLE lupus was recently noticed in a high interleukin10/low TNF alpha producer genotype (−1082 gg-308GG) [35]. A variant of the gene encoding the TRAF31P2, a member of the TNF receptor pathway involved in autoimmune diseases - missense substitution Thr438Asn - has been associated with discoid lupus and folliculitis decalvans [36]. Recently studies have identified 10 hub genes associated with CCLE which are CXCL10, CCR7, FPR3, PPARGC1A, MMP9, IRF7, IL2RG, SOCS1, ISG15 andGSTM3. Although general signs may be absent from skin in CCLE, it is a site of important disease activity. Genetic mapping recently showed overlapping of regions in seven (7) chromosomes - mainly genes of interferons and tumor necrosis factor-alpha between SLE and CCLE. In conclusion, these findings indicate that a genetic risk is shared by both SLE and CCLE [37, 38]. Micro RNA associated with epigenetic processes has also been found decreased in the serum of patients with CCLE [39].
